Biodiverse Walls - Design, Functioning, and Monitoring Methodology

According to the 2019 IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services) report, global ecosystems are facing an unprecedented crisis of biodiversity collapse, caused by human activities: destruction of terrestrial and marine habitats, direct exploitation, climate change, pollution and the spread of invasive species. This is having an alarming impact on the health of ecosystems, threatening living conditions on Earth, including those of human beings. Increasing urbanization is one of the major factors in the erosion of biodiversity, causing species to lose habitat through soil artificialisation, fragmentation and pollution. One way of reinforcing or restoring ecological continuity in cities, particularly where open space is in short supply, is to green the architecture. Buildings can provide refuges for biodiversity thanks to their envelopes – façades and roofs – which, according to Arnold Darlington in his book Ecology of Walls (1981), account for up to 50% of the total surface area of cities.

Although the greening of buildings has existed for millennia – it seems to have coincided with the emergence of architecture and the art of gardening – Today, the term "green walls" is used more specifically to designate wall greening systems. There are two main categories in the scientific literature. The first refers to green facades – Green Facades – and covers all solutions that include climbing plants such as ivy or vines. In the ground or in pots, plants grow either directly or indirectly – using cables or trellis – on a facade. These are referred to as "direct" or "indirect" green facades. These are generally simpler and more affordable than other systems, but are limited to climbing species. The second category, living walls – Living Walls Systems – refers to other, more complex solutions, which generally include small plants in the herbaceous stratum. These are divided into two main technical solutions: continuous walls and modular walls. In the former, plants grow in a continuous fabric, generally made of textile, thanks to a hydroponic ferti-irrigation system –. Nutrients are supplied to the plants by water via the sprinkler system. Modular living walls come in a variety of forms: perforated panels or panels divided into cells, stacked planters, wire mesh cages and so on. Most are installed as cladding on a façade.

This article examines the functioning of a new type of green wall, the "biodiverse" wall, which breaks away from existing categories in two major ways. The first is to enclose within the wall a continuous layer of living substrate, in which the plants on the facade grow. This layer is connected to open soil and, if possible, to a green roof. The aim is to increase soil interaction and biological activity, to promote the development...